Sylvia Plath and Ted Hughes’ tumultuous relationship has been widely discussed among scholars as The Bell Jar writer grappled with depression and mental illnesses.

In the letters, Plath accuses Hughes of beating her before miscarrying their second child in 1961.(Getty Images/Science Source)

Sylvia Plath alleged Ted Hughes beat her two days before she miscarried their second child and that Hughes wanted her dead, unpublished letters reveal. The two accusations are among explosive claims in unseen correspondence written in the bitter aftermath of one of literature’s most famous and destructive marriages.

Written between 18 February 1960 and 4 February 1963, a week before her death, the letters cover a period in Plath’s life that has remained elusive to readers and scholars alike. While the American writer, who was living in England during that time, was a prolific letter writer and had kept detailed journals since the age of 11, after her death Hughes said his wife’s journals from this time were lost, including the last volume, which he said he destroyed to protect their children, Frieda and Nicholas.

Sent to Dr Ruth Barnhouse – the model for Dr Nolan in Plath’s autobiographical novel The Bell Jar, who treated the writer in the US after her first documented attempt to kill herself in August 1953 – the correspondence is understood to be one of Plath’s only surviving uncensored accounts of her last months, in which she produced some of her most famous poetry, including the collection Ariel.

Nine letters written after Plath discovered her husband’s infidelity with their friend Assia Wevill in July 1962, form the core of the collection. The letters are part of an archive amassed by feminist scholar Harriet Rosenstein seven years after the poet’s death, as research for an unfinished biography. Also included in the collection are medical records from 1954, correspondence with Plath’s friends and interviews with Barnhouse about her therapy sessions with the poet. The archive came to light after an antiquarian bookseller put it up for sale for $875,000 (£695,000).

Plath’s treatment with Barnhouse ended when the poet moved to England but the two shared a close friendship, which has long been of interest to scholars because of their affection for one another. The correspondence reveals a warm and open intimacy, as well as a shared sense of humour.

But as well as exposing her pain at the discovery of Hughes’s adultery, the most shocking passages reveal Plath’s accusation of physical abuse shortly before miscarrying their second child in 1961, in a letter dated 22 September 1962 – the same month the poets separated. Several of Plath’s poems address her miscarriage, such as Parliament Hill Fields: “Already your doll grip lets go.”

The extent of their estrangement during this period is revealed in another letter in the collection, dated 21 October 1962, in which Plath claimed to Barnhouse that Hughes told her directly that he wished she was dead. Though Plath had a history of depression and self-harm, and had attempted to kill herself in 1953, she didn’t reveal the full extent of her struggles with mental health to Hughes until some time after their marriage.

The unseen letters were written at a time when Plath was troubled by her mental state, during the disintegration of one of the most famous literary romances of the 20th century. Yorkshire-born Hughes had met Plath, a Fulbright scholar, while they were students at Cambridge University in 1956. Hughes was already an established poet and she had gone to a party on 25 February of that year with the express desire to meet him. Within four months, they had married and the two quickly formed a formidable and mutually beneficial creative partnership that resulted in Hughes’s breakthrough Hawk in the Rain collection and Plath’s semi-autobiographical novel The Bell Jar.

Public fascination with their relationship has endured, in part because of how their creative output drew on their life experiences. During October 1962, Plath wrote the majority of the poems that would be included in Ariel – published posthumously in 1965 – which include many references and iconography often interpreted as being about Hughes. These include the lines in Daddy: “I made a model of you, / A man in black with a Meinkampf look / And a love of the rack and the screw.” Plath wrote to her mother during this period: “I am writing the best poems of my life. They will make my name.”

Reflecting on their relationship decades later in Birthday Letters, his 1998 collection about his time with Plath and the aftermath of her death, Hughes recalled their stormy liaison. The book was his final riposte to the feminist critics who, in the 70s, spoke out against Hughes over his treatment of Plath. During that time, he was interrupted with shouts of “murderer” at his readings; American feminist Robin Morgan published the poem The Arraignment, which began with the line “I accuse/Ted Hughes”. Plath was buried in a grave that read Sylvia Plath Hughes, at Hughes’s insistence. It was targeted by vandals who removed his name.

In his 1998 collection Howls and Whispers, Hughes quoted one of Barnhouse’s replies to Plath in September 1962, in the title poem: “And from your analyst: ‘Keep him out of your bed. Above all, keep him out of your bed.’” In 2010, Hughes’s apparent final word on the turbulent relationship was published in the form of his poem Last Letter, which described what happened in the three days before his wife died.

Plath scholars hailed the letters and archive as a remarkable source of new information about Plath, whose collected letters are soon to be published by Faber, with the first of two volumes due out on 5 October. Co-editor Peter K Steinberg said: “It’s an amazing collection of material that has been completely off the radar.”

Describing the letters, which he has not yet seen, as “tantalising”, he added that he expected them to reveal details that would otherwise be unknown in the absence of her journals and other letters. He hoped it would be possible to include the newly discovered material in volume two. Citing the “sensational” poetry Plath wrote in October 1962, including The Detective, the Bee poems, and Ariel, he said: “It is possible that Plath found catharsis in writing out to Dr Barnhouse; and that in doing so it freed her to write those explosive, lasting poems.”

Andrew Wilson, author of Mad Girl’s Love Song, about Plath’s life before she met Hughes, said the interviews with Barnhouse would provide an invaluable insight into the origins of her battle with depression and were the “missing link” in her biography and literary history. “These letters look as though they could fill certain gaps in our knowledge, and seem as though they can shed new light on the turbulent, controversial marriage between Plath and Hughes,” he said.

The archive first came to the attention of Plath scholars after a rare books seller advertised it online for sale on behalf of Rosenstein, with the collection also featured as part of the New York antiquarian book fair in March. However, the letters may not see the light of day for quite some time. Smith College, Plath’s alma mater, filed a lawsuit on 12 March claiming the letters were part of the Barnhouse estate that was bequeathed to it after her death. Rosenstein maintains she was given the letters 47 years ago by Barnhouse. Until the lawsuit is settled, the letters have been taken off the market.